Dorothy Nickerson

FINAL REPORT OF THE O.S.A. SUBCOMMITTEE ON SPACING OF THE MUNSELL COLORS

This report presents the characteristics of a modified and enlarged Munsell solid which has been evolved from the 1940 visual estimates of the Munsell Book of Color samples. All three dimensions have been carefully reviewed and extensively revised. The newly defined loci of constant hue have been extended closer to the extremes of value while the loci of constant chroma have been extrapolated to the pigment maximum. The dimension of value has been redefined without substantial departure from the Munsell-Sloan-Godlove scale. By the above changes a solid is achieved which approaches more closely to A. H. Munsell’s dual ideal of psychological equispacing and precise applicability. The new solid is defined in terms of the I.C.I. standard coordinate system and Illuminant C.

Tristimulus Specification of the Munsell Book of Color from Spectrophotometric Measurements

The development of the Inter-Society Color Council-National Bureau of Standards (ISCC-NBS) system of color names, based on the standards in the Munsell Book of Color, made it necessary to specify the master standards of this book in fundamental terms. Accordingly, spectral reflection curves were run for each of the 421 master standards on the General Electric recording spectrophotometer at the National Bureau of Standards, using slit widths of approximately 4 millimicrons. Various corrections were applied to these spectrophotometric data in accordance with methods regularly used for such work at the bureau. Colorimetric computations were then made with these data, resulting in tristimulus specifications according to the 1931 ICI standard observer and coordinate system. Four illuminants were used: ICI Illuminants A and C, representative of incandescent-lamp light and average daylight, respectively, Illuminant D (lightly overcast north sky), and Illuminant S (extremely blue sky). The colorimetric specifications of the Munsell standards for all four illuminants are thus given. The trilinear coordinates for the Munsell standards calculated for ICI Illuminant C have been plotted on large chromaticity (x, y) diagrams and constant Munsell chroma lines drawn in. (Similar values obtained by Glenn and Killian at the Massachusetts Institute of Technology in 1935 for Munsell color standards bearing the same hue-value-chroma designations have also been plotted on the diagram and differences between the two sets of data are discussed.) These diagrams serve as means for determining the Munsell notation and thereby the ISCC-NBS color name for any color whose trilinear coordinates and apparent reflectance are given.

The Specification of Color Tolerances

. by eye (used by expert matchers, elnssers, and graders) to coniparisons of measurements made on beautifully adjusted, highly intricate, automatic, instruments. Between these extremes are a great variety of instruments by means of which tlie colors may be compared. Measurements made on such instruments are expressed in a wide variety of terms. Some results arc expressed directly in terms of instrument opl’ration, c.,g., in terms of particular filters used in the instrument. Others

Light Sources and Color Rendering

Light sources for many problems in agriculture and industry require good color rendering; standards are needed for both special and general purpose lamps. Target standards are discussed, and color, relative spectral distributions, and lumen efficiency data are provided for typical incandescent and fluorescent lamps. Data for color samples calculated for triads of light sources studied by an I.E.S. Subcommittee on Color Rendition of Light Sources are used to demonstrate the comparative size and direction of color differences involved in common situations. Problems raised by chromatic adaptation are discussed, as are specifications and standards for sources used for color work in various specialized industries, and the progress being made by I.E.S. and CIE committees on color rendering.

Munsell renotations for samples of OSA uniform color scales

Munsell renotations for the OSA-UCS set of 558 samples are given in two tables: One provides conversions for the 424 basic colors of the set; the other provides conversion for the additional 134 half-step samples.

Munsell Renotations Used to Study Color Space of Hunter and Adams

The calorimetric scales of recent Hunter and Adams proposals are studied in terms of the smoothed curves of the Munsell renotation space. Three conversion tables prepared provide: I.C.I. (X, Y, Z) data; Adams’ chromatic value data; Hunter’s a and b. Each table extends to the theoretical hue, value, and chroma limits of the original table. Such use of Munsell renotation data makes it possible to visualize the color spacing of the coordinates of any color measuring instrument that is based upon or related to the I.C.I. system, and makes it possible to understand instrument results in terms of color experience, and thus assess the accuracy and precision of an instrument in terms of standard colorimetric practice and known color tolerance.

Color Measurements of Standards for Grades of Cotton

Measurements of the color of standards for grades of cotton, which were made in the United States Department of Agriculture, are shown in a series of diagrams. These illustrate the relation of the grades to each other in color, how the color may change during a period of years, and color measurements of the original standards, copies of them, and of the standards adopted in 1946 to become effective August 1, 1947.

Colorimetric Specifications of Munsell Repaints

A table of C.I.E. tristimulus values and chromaticity coordinates, and Munsell renotations is provided for repaints of all regular Munsell standard papers made up to July, 1950, that have not been reported previously. The colorimetric data were calculated from spectrophotometric measurements.

New Automatic Colorimeter for Cotton

This new instrument for measuring the color of cotton is based on a satisfactory application of the Hunter Color and Color-Difference Meter to problems of raw cotton measurement. It is designed to be fully automatic and self-standardizing, and graphically to show values for reflectance (Rd) and yellowness (+b) on a two-dimensional chart. It is self-contained in a movable cabinet, with a minimum of exposed parts. Although this particular model is limited to measurements in the range of cotton color, the principles on which it is designed are adaptable to other limited ranges of color, in either two or three dimensions, thus providing an automatic, self-standardizing small-difference colorimeter for other limited ranges of color.

Uniform color scales: Munsell conversion of OSA committee selection

Rhombohedrally arranged colors selected by the OSA Committee on Uniform Color Scales have been converted to Munsell renotations and are shown on Munsell Hue–Chroma diagrams for several planes of OSA Committee lightness.